If You Build It Will They Come? Associations Between Birds and Vegetation Structure During Ten Years After Thinning Sveta Yegorova, Drs. Matt Betts, Joan.

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Presentation on theme: "If You Build It Will They Come? Associations Between Birds and Vegetation Structure During Ten Years After Thinning Sveta Yegorova, Drs. Matt Betts, Joan."— Presentation transcript:

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If You Build It Will They Come? Associations Between Birds and Vegetation Structure During Ten Years After Thinning Sveta Yegorova, Drs. Matt Betts, Joan Hagar* and Klaus Puettmann Department of Forest Ecosystems and Society, Oregon State University * U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, Corvallis, OR Corvallis, Oregon 97330 USA USGS, Corvallis, Oregon Background Methods Results Discussion Hypotheses I.Vegetation effects varied among years and were inconsistent in size II.In some years vegetation models performed well (e.g., MacGillvrays Warbler and Golden-crowned Kinglet, see figures 1 and 2 below) III.Changing population sizes may explain varying model fits Figure 1. MacGillivrays Warbler: Occupancy by Shrub Cover Figure 2. Golden-crowned Kinglet: Occupancy by Conifer Density Quantifying Variability of Vegetation/Treatment Effect on Occurrence We used the ratio of variable estimate to its standard error (GOF=Estimate/SE(Estimate)) to quantify the variability of the size of the effect. GOF appears to be highly variable even for species associated with vegetation structures (as in Fig. 1 and 2) in some years. See figures 3-6 for illustration. Forest thinning encourages understory and overstory development in young Douglas-fir forests Effects of thinning on birds have been shown to vary by species and with time since thinning These effects are assumed to be mediated by the residual vegetation structure but this assumption is rarely tested Alternatively, habitat selection may be driven by other (non-vegetation) factors, including previous experience, social information, and density of conspecifics Therefore disturbance (thinning) may cause a lag in bird- vegetation association Large population size may result in poor fit between bird occurrence and vegetation structure due to population spillover into low quality habitat I.If vegetation drives bird occurrence, then a. There will be strong associations between bird occurrence and vegetation structure immediately after thinning b. These associations will be consistent over time II. If other factors are contributing to habitat selection there may be high year-to-year variability in bird-vegetation associations 30-50 yr old Douglas-fir stands Mid-elevation (500-900ft) forests on west slopes of the central Cascade Mountains in Oregon Detailed understory and overstory vegetation measurements taken four times since thinning Breeding season point count surveys conducted six times Analysis We selected best performing model, using Akaike Information Criterion (AIC), from a priori set pool of models that reflects the hypotheses stated above. Bird-vegetation associations appear to be highly variable in this long- term (10 years) study. Single-season bird surveys are unlikely to properly reflect an underlying relationship between bird occurrence and vegetation structure. Our results suggest that population size, for abundant species, and possibly social factors interact with vegetation structure to produce observed bird occurrence patterns. TreatmentDensity (trees per hectare) Heavy125 Light250-300 Light with Gaps250-300 with 0.2 ha gaps Control650 Occurrence of eight species was modeled as a function of vegetation structure or treatment (fixed effects) and block and stand (random effects) using mixed-effects logistic regression. Analysis continued MacGillivrays Warbler Swainsons Thrush Golden-crowned Kinglet Hammonds Flycatcher Cumulative GOF Graphs Figure 6 Hammonds Flycatcher Figure 5 Swainsons Thrush Figure 4 MacGillvrays Warbler Figure 3 When pooled across species, GOF is associated negatively with abundance for relatively abundant species (Fig 6). GOF did not correlate with time since thinning (data not shown). Hammonds Flycatcher Golden-crowned Kinglet Figure 1 Figure 2